Discharging stored EGR in boosted engine system

ABSTRACT

A method for controlling an engine with exhaust gas recirculation is provided. The method comprises directing EGR from exhaust downstream of an exhaust-aftertreatment catalyst to mix with fresh air upstream of an intake compressor and upstream of a throttle valve, and, in response to increased throttling by the throttle valve, discharging the mixed EGR and fresh air from downstream of the intake compressor to the exhaust downstream of the exhaust-aftertreatment catalyst.

TECHNICAL FIELD

The present application relates to improving fuel economy and reducingemissions in motor vehicles, and more particularly, to enactingexhaust-gas recirculation in boosted engine systems.

BACKGROUND AND SUMMARY

A boosted engine may exhibit higher combustion and exhaust temperaturesthan a naturally aspirated engine of similar output power. Such elevatedtemperatures may contribute to increased nitrogen-oxide (NOX) emissionsand may accelerate materials ageing in the engine system, includingexhaust-aftertreatment catalyst ageing. Exhaust-gas recirculation (EGR)is a popular strategy for combating these effects. EGR works bydelivering exhaust gas having reduced oxygen content to the intake,which results in lower combustion and exhaust temperatures. Inparticular, EGR variants that deliver cooled EGR are desirable becausethey can supply a relatively large flow of exhaust gas to the intake.However, cooled EGR is liable to cause transient control difficulties inboosted engine systems, particularly in combination with spark-ignition.For instance, throttle closure in a system configured for cooled EGR maytrap a significant volume of compressed, EGR-diluted air upstream of thethrottle. Such trapping may occur on transitioning from high to lowengine load, for example. Under low-load, closed-throttle conditions,however, the engine may require fresh air to sustain combustion. Openinga compressor by-pass valve at this time provides a partial, butincomplete remedy for the problem, as the EGR-diluted air remainsupstream of the throttle, albeit at a lower absolute pressure.

Excess intake pressure may be vented to other locations of an enginesystem besides the compressor inlet. Accordingly, U.S. Pat. No.5,724,813 provides a compressor bypass valve that vents pressurizedintake air upstream of a throttle to an exhaust conduit immediatelyupstream or immediately downstream of a turbocharger turbine. However,this system is not suitable for improving transient control in a modernengine system equipped with cooled LP EGR, as it lacks both an EGRsystem and an exhaust-aftertreatment system.

The inventors herein have recognized that improved transient control inan LP EGR equipped engine system can be achieved by judiciouslyconfiguring compressed air release with respect to EGR andexhaust-aftertreatment components. In one embodiment, therefore, amethod for controlling an engine with exhaust gas recirculation isprovided. The method comprises directing EGR from exhaust downstream ofan exhaust-aftertreatment catalyst to mix with fresh air upstream of anintake compressor and upstream of a throttle valve, and, in response toincreased throttling by the throttle valve, discharging the mixed EGRand fresh air from downstream of the intake compressor to the exhaustdownstream of the exhaust-aftertreatment catalyst.

In this manner, a significant amount of pressurized, EGR-diluted airfrom behind the throttle can be quickly eliminated, thereby alleviatingat least some transient-control difficulties associated with cooled LPEGR. Further, the disclosed methods avoid release of untreated exhaustinto the ambient, and further avoid damage to compressor components dueto soot entrained in recirculated exhaust gasses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-4 show aspects of systems configured to provide intake air to anengine in a vehicle, in accordance with different embodiments of thepresent disclosure.

FIGS. 5-9 illustrate methods for providing intake air to an engine in avehicle, in accordance with different embodiments of the presentdisclosure.

DETAILED DESCRIPTION

The subject matter of the present disclosure is now described by way ofexample and with reference to certain illustrated embodiments.Components that may be substantially the same in two or more embodimentsare identified coordinately and are described with minimal repetition.It will be noted, however, that components identified coordinately indifferent embodiments of the present disclosure may be at least partlydifferent. It will be further noted that the drawings included in thisdisclosure are schematic. Views of the illustrated embodiments aregenerally not drawn to scale; aspect ratios, feature size, and numbersof features may be purposely distorted to make selected features orrelationships easier to see.

FIG. 1 shows aspects of a first example system 10 configured to provideintake air to an engine 12 in a vehicle. The engine includes a pluralityof combustion chambers 14, each coupled to intake manifold 16 and toexhaust manifold 18. In the combustion chambers, combustion may beinitiated via spark ignition and/or compression ignition in any variant.Further, the engine may be configured to consume any of a variety offuels: gasoline, alcohols, diesel, biodiesel, compressed natural gas,etc. The fuel may be supplied to the combustion chambers via directinjection, port injection, or any combination thereof.

System 10 is configured to supply compressed intake air to engine 12during certain operating conditions. Accordingly, fresh air enters thesystem via air cleaner 20 and flows to compressor 22. The compressor maybe any suitable intake-air compressor—a drive-shaft driven ormotor-driven supercharger compressor, for example. In the embodimentshown in FIG. 1, the compressor is a turbocharger compressormechanically coupled to turbine 24, the turbine driven by expandingengine exhaust from exhaust manifold 18. From compressor 22, compressedintake air flows through intercooler 26 en route to throttle valve 28.The intercooler may be any suitable heat exchanger configured to coolthe intake air for desirable combustion properties.

As noted above, exhaust from exhaust manifold 18 flows to turbine 24 todrive the turbine. When reduced turbine torque is desired, some exhaustmay be directed instead through waste gate 30, by-passing the turbine.The combined flow from the turbine and the waste gate then flows throughexhaust-aftertreatment devices 32, 34, and 36. The nature, number, andarrangement of the exhaust-aftertreatment devices may vary in thedifferent embodiments of the present disclosure. In general, theexhaust-aftertreatment devices may include at least oneexhaust-aftertreatment catalyst configured to catalytically treat theexhaust flow, and thereby reduce a concentration of one or moresubstances in the exhaust flow. For example, one exhaust-aftertreatmentcatalyst may be configured to trap nitrogen oxides (NOX) from theexhaust flow when the exhaust flow is lean, and to reduce the trappedNOX when the exhaust flow is rich. In other examples, anexhaust-aftertreatment catalyst may be configured to disproportionateNOX, or, to selectively reduce NOX with the aid of a reducing agent. Inother examples, an exhaust-aftertreatment catalyst may be configured tooxidize residual hydrocarbons and/or carbon monoxide in the exhaustflow. Different exhaust-aftertreatment catalysts having any suchfunctionality may be arranged in wash coats or elsewhere in theexhaust-aftertreatment devices, either separately or together. In someembodiments, the exhaust-aftertreatment devices may include aregenerable soot filter configured to trap and oxidize particulates inthe exhaust flow.

Continuing in FIG. 1, part of the treated exhaust flowing fromexhaust-aftertreatment devices 32, 34, and 36 is released into theambient. However, the balance of the treated exhaust is drawn into EGRconduit 38 and flows through EGR cooler 40. The EGR cooler may be anysuitable heat exchanger configured to cool the treated exhaust flowingthrough the EGR conduit to temperatures suitable for mixing into theintake air. System 10 further includes variable venturi 42 coupledbetween air cleaner 20 and compressor 22. The variable venturi drawstreated exhaust from the EGR conduit, and mixes the treated exhaust intothe fresh air flowing in from the air cleaner. In one embodiment, thevariable venturi may be configured to conduct the fresh air axiallythrough an expansion chamber, in which a partial vacuum caused by theexpanding flow draws in the treated exhaust through an eccentric inlet.Meanwhile, the amount of treated exhaust available for mixing into thefresh air is regulated via EGR valve 44. A mixture of fresh air andtreated exhaust may be provided, accordingly, as intake air to the inletof the compressor.

FIG. 1 shows pressure sensor 46 coupled to the upstream side of throttlevalve 28. The pressure sensor may be one of a plurality of sensors(pressure sensors, temperature sensors, etc.) coupled throughout theengine system. The pressure sensor may be configured to provide anoutput responsive to the air pressure at the upstream side of thethrottle valve, i.e., the throttle inlet pressure (TIP). Under someoperating conditions, it may be desirable to abruptly reduce TIP. Suchconditions may include, for example, full or partial closure of thethrottle valve. Accordingly, FIG. 1 shows release valve 48 coupling theupstream side of the throttle valve to the downstream side ofexhaust-aftertreatment device 36, via release conduit 50. As shown inFIG. 1, the release valve may be coupled to the downstream side ofexhaust-aftertreatment device 36 via an optional check valve 52. In oneembodiment, the release valve may be a two-state valve having an openposition and a closed position. In other embodiments, however, therelease valve may admit of a variable (e.g., continuously adjustable)degree of opening.

In some embodiments check valve 52 may be included to prevent exhaustfrom flowing through release valve 48 to throttle valve 28 underconditions of low TIP. In other embodiments, however, such exhaust flowmay be desired under appropriate operating conditions. Thus, check valve52 may be omitted in certain embodiments, and release valve 48 may beused to regulate a flow of exhaust (i.e., EGR) to the upstream side ofthrottle valve 28. Accordingly, a second EGR cooler (not shown in thedrawings) may be disposed between the release valve and the throttlevalve and configured to cool the treated exhaust flowing through releaseconduit 50. In still other embodiments, the release conduit may becoupled to the upstream side of intercooler 26 instead of the downstreamside, allowing the EGR to be cooled via the intercooler instead of asecond EGR cooler.

In some embodiments, throttle valve 28, waste gate 30, EGR valve 44,and/or release valve 48 may be electronically controlled valvesconfigured to close and open at the command of an electronic controlsystem. Further, one or more of these valves maybe continuouslyadjustable. Accordingly, FIG. 1 shows electronic control system 54,which may be any electronic control system of the vehicle in whichsystem 10 is installed. The electronic control system may be operativelycoupled to each of the electronically controlled valves and configuredto command their opening, closure, and/or adjustment as needed to enactany of control functions described herein. In one embodiment, theelectronic control system may be configured to open the release valve inresponse to a closure of the throttle valve, and to close the releasevalve when TIP falls below a threshold value, as further describedbelow. To this end, the electronic control system may be operativelycoupled to various sensors arranged throughout the illustratedsystem—temperature sensors, pedal-position sensors, pressure sensors,etc., including pressure sensor 46.

Various advantages of the approaches described herein are bestunderstood in contrast to existing compressor-control configurations,which, upon throttle closure, reduce TIP by venting pressurized intakeair from upstream of the throttle valve back to the compressor inlet viaa compressor by-pass valve. Should such venting occur when the enginehas been operating at a significant EGR ratio, exhaust gas presentupstream of the throttle valve before venting will remain at the sameratio after venting, albeit at a lower absolute pressure. However,sustained combustion under closed-throttle conditions will typicallyrequire fresh intake air having little or no EGR. Therefore, theexisting configurations may be prone to combustion instability in thiscommon scenario.

The embodiment shown in FIG. 1 overcomes the disadvantage noted above byallowing pressurized intake air to be discharged into the exhaust flowinstead of the compressor inlet. In this manner, intake air upstream ofthrottle valve 28 is effectively purged of exhaust gas, and is replacedby fresh air from air cleaner 20. Such fresh air reliably supportscombustion under low engine-load (e.g., closed-throttle) conditions.

The inventors herein have recognized, however, that releasing intake airinto the exhaust flow, even when diluted significantly by EGR, couldadversely affect exhaust-aftertreatment catalysts arranged in theexhaust flow. Therefore, the embodiment shown in FIG. 1 provides thatthe compressed mixture of fresh air and treated exhaust may be releaseddownstream of exhaust-aftertreatment devices 32, 34, and 36. To avoiddischarge of untreated exhaust to the ambient during the release, theembodiment also provides that the EGR is drawn from the exhaust flowdownstream of the exhaust-aftertreatment devices. In embodiments wheresuch exhaust-aftertreatment devices include a soot filter, it is furtherprovided that the EGR will not entrain excessive amounts of soot, whichcould potentially damage compressor 22 and EGR cooler 40. It will befurther noted that the embodiment shown in FIG. 1 overcomes thedisadvantages of existing configurations using the same number ofelectronically controlled valves as found in the existingconfigurations: release valve 48 merely replaces the compressor by-passvalve.

FIG. 1 illustrates one of many embodiments contemplated herein; relatedembodiments, fully consistent with the present disclosure, may beconfigured differently. For example, some embodiments may include ahigh-pressure exhaust-gas recirculation (HP EGR) path in addition to theillustrated LP EGR path. Still other embodiments may lack variableventuri 42, and may provide alternative componentry for mixing EGR intothe inlet air flow.

FIG. 2 shows aspects of a second example system 56 configured to provideintake air to an engine 12 in a vehicle. System 56 differs from system10 in that unwanted EGR is here released upstream ofexhaust-aftertreatment device 36, which may be a regenerable sootfilter. This configuration offers an advantage in that the release ofunwanted EGR may, under some conditions, be coordinated with oxidativeregeneration of the soot filter. In particular, an excess quantity ofcompressed air may be delivered to the soot filter to support suchregeneration, while more upstream exhaust-aftertreatment catalysts (32and 34, for example) continue to operate under stoichiometricconditions.

FIG. 3 shows aspects of a third example system 58 configured to provideintake air to an engine 12 in a vehicle. In the embodiment shown in FIG.3, air is supplied to intake manifold 16 via first throttle valve 28, asdescribed in the previous embodiment, and via second throttle valve 60.The first and second throttle valves may be coupled directly to theintake manifold, as shown in the drawing, or coupled indirectly via anysuitable componentry. Depending on operating conditions, the firstthrottle valve may regulate a flow of boosted air and/or air containingEGR. Meanwhile, the second throttle valve regulates a flow ofuncompressed, fresh air from air cleaner 20 to intake manifold 16.

As in the previous embodiment, electronic control system 54 may beoperatively coupled to various engine system sensors, including amanifold air-pressure sensor or other sensor configured to determineengine torque or any quantity responsive to changing engine load. Thus,by appropriate operative coupling to controller 54, the first throttlevalve may be configured to open during a higher engine-load condition toadmit boosted and/or EGR-containing air to intake manifold 16. Likewise,the second throttle valve may be configured to open during a lowerengine-load condition to admit fresh air to the intake manifold. In thismanner, the configuration shown in FIG. 3 provides another approach tomaintaining combustion stability during abrupt engine-load reduction ina boosted engine system. In particular, abrupt reduction in engine loadmay trigger a closure of first throttle valve 28, thus trapping unwantedEGR behind the first throttle valve. Such engine-load reduction may berevealed by a corresponding reduction in MAP, for example. During thiscondition, undiluted fresh air may be delivered to the engine via secondthrottle valve 60, to reliably support combustion.

In one embodiment, first throttle valve 28 and second throttle valve 60may be substantially the same. They may be state-of-the-art,electronically actuated throttle valves. In other embodiments, the firstand second throttle valves may be at least partly different. Forexample, the second throttle valve may be an idle air by-pass valve(IABV) variant configured to withstand greater-than-normal air flowsand/or back pressure. As such, the second throttle valve may beconfigured for relatively fine control of the air flow, as may berequired during idle conditions and thereabouts. By controlling air flowvia the second throttle valve during conditions where relatively fineair-flow control is needed, a lesser control precision of the firstthrottle valve may be tolerated. In one embodiment, —accordingly, thefirst throttle valve may include a bore having a relatively large crosssection, which is advantageous for controlling air flow during high-loadconditions, where a relatively large flow of boosted air and EGR may beinducted into the engine.

In one embodiment, second throttle valve 60 may be held closed duringboosted conditions to prevent depressurization of the intake manifoldand reverse flow through air cleaner 20. In other embodiments, as shownin FIG. 3, optional check valve 62 may be coupled in series with thesecond throttle valve to passively prevent such depressurization.

In another embodiment, backflow through second throttle valve 60 may bereduced by keeping the length of the conduit between the second throttlevalve and venturi 42 relatively short, such that any backflow—includingbackflow containing EGR—will be swept into the venturi. Thus, whenforward flow through throttle valve 60 is desired, it will besubstantially free of EGR.

Further, the embodiment illustrated in FIG. 3 provides still anotheradvantage, in that the EGR trapped behind the first throttle valve, asindicated above, is not necessarily dissipated immediately at TIP out,but may remain available, i.e., stored, for uptake during subsequent TIPin.

Continuing in FIG. 3, system 58 shows compressor by-pass valve 64configured to discharge excess compressed intake air upstream of firstthrottle valve 28 back to the inlet of compressor 22. Electronic controlsystem 54 may command the by-pass valve to open during a reduction ofengine load, for example. It will be understood, however, that otherembodiments fully consistent with this disclosure may include a releasevalve coupled as shown in the previous embodiments (e.g., FIG. 1,release valve 48).

It will be understood that no aspect of FIG. 3 is intended to belimiting. For example, EGR may be drawn from downstream ofexhaust-aftertreatment device 36, as shown in FIG. 3, or, it may bedrawn from upstream of any of the exhaust-aftertreatment devices ofengine system 58.

FIG. 4 shows aspects of a fourth example system 66 configured to provideintake air to an engine 12 in a vehicle. System 66 includesheat-exchanger 68, which may be any passive device suitable foradjusting a temperature of a gas flowing therethrough. The drawing showsintake manifold 16 coupled directly to first throttle valve 28 andsecond throttle valve 60. In other embodiments, the first and secondthrottle valves may be coupled to the intake manifold indirectly, viaany suitable componentry. As shown in FIG. 4, the outlet of the heatexchanger is coupled to the intake manifold via second throttle valve60. Accordingly, the heat exchanger may be configured to adjust thetemperature of the gas to enable desirable combustion performance inengine 12. Warming and cooling the gas are both enabled and may beenacted in the same system during different operating conditions, asfurther described below.

During conditions of relatively high engine load, the gas inside heatexchanger 68 may comprise EGR destined for delivery to the engineintake; accordingly, the heat exchanger may be adapted to lower thetemperature of the EGR, thereby serving as an EGR cooler. Duringconditions of relatively low engine load, the gas inside the heatexchanger may comprise fresh air, also destined for delivery to theengine intake; accordingly, the heat exchanger may be adapted to raisethe temperature of the fresh air, thus serving as an intake air heater.Intake-air heating may improve the overall efficiency of the engineunder light-load conditions by decreasing pumping losses, for example.

In one embodiment, heat exchanger 68 may conduct air and EGR through agas conduit, and may also conduct a liquid through a liquid conduit. Thegas and liquid conduits may be thermally coupled but fluidicallyisolated from each other. In one embodiment, engine coolant may beconducted through the liquid conduit. Accordingly, the heat exchangermay be configured to conduct heat from the EGR flow to the enginecoolant during the higher engine-load condition, and to conduct heatfrom the engine coolant to a fresh air flow during the lower engine-loadcondition.

Continuing in FIG. 4, system 66 shows control valve 70, which isoperatively coupled to electronic control system 54. As indicated withrespect to the previous embodiments, the electronic control system maybe operatively coupled to various engine system sensors responsive tochanging engine load. Accordingly, under higher engine-load conditions,where EGR and boost are desired, control valve 70 may be held closed andEGR valve 44 may be held open. In the illustrated configuration, closingthe control valve and opening the EGR valve causes EGR to flow from EGRconduit 72 through heat exchanger 68 and simultaneously blocks the flowof fresh air to the heat exchanger. Under these conditions, compressor22 receives and compresses a flow of fresh air, and delivers thecompressed fresh air flow to first throttle valve 28. Further, the EGRvalve regulates and delivers an EGR flow to second throttle valve 60.Cooled, EGR is thereby provided to intake manifold 16 via the secondthrottle valve, while fresh air from air cleaner 20 is provided,compressed and cooled, to the intake manifold via the first throttlevalve. Thus, the first throttle valve is used to meter compressed, freshair, and the second throttle valve is used to meter EGR.

Under conditions where neither EGR nor boost are desired, control valve70 may be held open, and EGR valve 44 may be held closed. Opening thecontrol valve and closing the EGR valve allows fresh air to flow throughheat exchanger 68, and simultaneously blocks admission of EGR to theengine intake. Warmed, fresh air is thereby provided to intake manifold16 via second throttle valve 60, while first throttle valve 28 is heldclosed. In this manner, the second throttle valve may be used to meterair flow into engine 12.

The embodiment illustrated in FIG. 4 provides still other advantages.During TIP-out conditions, when a significant amount of unwanted,compressed intake air may be trapped upstream of first throttle valve28, opening first throttle valve 28, second throttle valve 60, andcontrol valve 70 provides a blow-off mechanism for compressor 22. Inthis manner, excess boost pressure may be routed back to the compressorinlet when EGR valve 44 is closed.

No aspect of FIG. 4 is intended to be limiting, for numerous relatedembodiments are contemplated. For example, while a single heat exchanger68 may be used to cool EGR and to warm intake air, these functions may,in other embodiments, be accomplished via separate, coupled or uncoupledheat exchangers. Further, either or both of the heat exchangers may useair instead of, or in addition to engine coolant, as a medium to whichheat from the EGR is transferred.

In contrast to the engine systems of FIGS. 1-3, which provide cooledlow-pressure EGR, the configuration shown in FIG. 4 also provides cooledhigh-pressure EGR. It will be understood, however, that this embodimentmay be combined, generally, with suitable low-pressure EGR approaches inthe same engine system. Such integrated low- and high-pressure EGRsystems may include aspects of the embodiments shown in FIGS. 1-3 anddescribed hereinabove. In a system that supports both a low-pressure anda high-pressure EGR path, two EGR valves may be included, with eachvalve configured to open during a predetermined higher engine-loadcondition. Further, the particular conditions that trigger the openingof the first EGR valve may differ from those that trigger the opening ofthe second EGR valve.

The configurations illustrated above enable various methods forproviding intake air to an engine in a vehicle. Accordingly, some suchmethods are now described, by way of example, with continued referenceto the above configurations. It will be understood, however, that themethods here described, and others fully within the scope of the presentdisclosure, may be enabled via other configurations as well.

FIG. 5 illustrates a first example method 76 for providing intake air toan engine in a vehicle. The method may be enacted via an electroniccontrol system (e.g., electronic control system 54) coupled to one ormore sensors and electronically controlled valves, as described above.For example, method 76 may be enabled via the configuration shown inFIG. 1.

Method 76 begins at 78, where a mixture of fresh air and treated exhaustis formed. The treated exhaust may be drawn from an exhaust flow of theengine downstream of an exhaust-aftertreatment catalyst, and, in someembodiments, a soot filter. The mixture may be formed by flowing thefresh air through a variable venturi, and admitting the treated exhaustto an eccentric inlet of the variable venturi from an EGR conduit, asdescribed hereinabove.

Method 76 advances to 80, where the mixture formed at 78 is compressedand delivered upstream of a throttle valve coupled into an intake of theengine. In one embodiment, the mixture may be compressed via aturbocharger compressor. The method then advances to 82, where aposition (i.e., degree of closure) of the throttle valve is sensed. Themethod then advances to 84, where it is determined, based in part on theposition sensed at 82, whether the throttle valve is closing—whetherfully closing or partially closing. If it is determined that thethrottle valve is not closing, then execution of the method resumes at82. However, if it is determined that the throttle valve is closing oris partially closing, then the method advances to 86, where the releasevalve is opened and held open. The release valve may be any valveswitchably coupling the upstream side of the throttle valve to thedownstream side of an exhaust-aftertreatment catalyst, as shownhereinabove. In this manner, in response to an increased closure (i.e.,throttling) of the throttle valve, the compressed mixture of fresh airand treated exhaust accumulated upstream of the throttle valve may bedischarged into the exhaust flow of the engine. In other embodiments,discharge of the compressed mixture into the exhaust flow may becorrelated to full or partial closure of the throttle valve, withoutbeing enacted in response to the closure per se. Further, the particularlocus of the exhaust flow where the intake air is discharged may bedownstream of the exhaust-aftertreatment catalyst. In some embodiments,the inlet air may be discharged downstream of everyexhaust-aftertreatment catalyst situated in the exhaust flow. In stillother embodiments, the inlet air may be discharged downstream of someexhaust-aftertreatment catalysts, but upstream of a soot filter, asfurther described hereinafter.

Method 76 then advances to 88, where an EGR valve regulating a flowtreated exhaust to the engine intake is closed. In this manner, treatedexhaust is restricted from mixing with the fresh air in response toclosure of the throttle valve. Method 76 then advances to 90, where thethrottle inlet pressure (TIP) is sensed. In one embodiment, TIP may besensed via a dedicated pressure sensor coupled to the upstream side ofthe throttle valve. The method then advances to 92, where it isdetermined whether TIP is within a predetermined interval of thepressure of the exhaust flow at the downstream side of anexhaust-aftertreatment catalyst. The predetermined interval may be anysuitable value defined in absolute terms (5 mm Hg, 10 mm Hg, etc.) orrelative to at least one of the compared pressures (+2%, +5%, etc.). Inmaking this determination, the electronic control system may sense ormerely predict the pressure of the exhaust flow—such pressure may bepredicted based on a known mass air flow through the engine, forexample.

If it is determined that the TIP is not yet within the predeterminedinterval of the pressure of the exhaust flow at the downstream side ofthe exhaust-aftertreatment catalyst, then execution of the methodresumes at 90. However, if it is determined that TIP is within thepredetermined interval, then the method advances to 94, where therelease valve is closed. In this manner, the release valve may be heldopen until, and closed after, a pressure at the upstream side of thethrottle valve and a pressure at the downstream of theexhaust-aftertreatment catalyst differ by less than a predeterminedamount. Following 94, method 76 returns. Engine operation may thencontinue with the release valve and the EGR valve both closed until suchtime as the electronic control system determines that EGR may again betolerated.

The foregoing method demonstrates that full or partial throttle closuremay be used to trigger the opening of the release valve and thatsubsequent closure of the release valve may be responsive to decreasingTIP. In other embodiments, however, other operating conditions of theengine may be used to determine one or more of an extent of opening anda duration of opening of the release valve. Decreasing acceleratordepression may be used instead of throttle closure to trigger theopening of the release valve, for example. Further, the position of theaccelerator may be used to determine the degree of opening of therelease valve. Moreover, the extent or duration of opening of therelease valve may be based on a measured or predicted EGR ratio upstreamof the throttle valve. For instance, the release valve may open wider orstay open longer when the EGR ratio is high, and may close as the EGRratio decreases. In still other embodiments, the extent or duration ofopening of the release valve may be based at least partly on enginespeed—the release valve opening wider or staying open longer when theengine speed decreases to lower RPM.

FIG. 6 illustrates a second example method 96 for providing intake airto an engine in a vehicle. The method may be enacted via an electroniccontrol system (e.g., electronic control system 54) coupled to one ormore sensors and electronically controlled valves, as described above.For example, method 96 may be enabled via the configuration shown inFIG. 2 in combination with other configurations described herein, forexample.

Method 96 begins at 82, where the position of the throttle valve issensed. The method then advances to 84, where it is determined whetherthe throttle valve is closing. If it is determined that the throttlevalve is not closing, then execution of the method resumes at 82.However, if it is determined that the throttle valve is closing or ispartially closing, then the method advances to 98, where it isdetermined whether a soot filter coupled in the exhaust system is readyfor regeneration.

In one embodiment, the determination at 98 may be made based on ameasured or predicted temperature in the exhaust system of the vehicle.For example, it may be determined that the soot filter is ready forregeneration if and only if the temperature is above a threshold, e.g.,the light-off temperature of a catalytic wash coat of the soot filter.In another embodiment, the determination may be made based on a measuredor predicted pressure difference between the inlet and the outlet of thesoot filter. For example, it may be determined that the soot filter isready for regeneration if the pressure difference is above a threshold.In still other embodiments, the determination at 98 may be based on acombination of these and other conditions.

Continuing in FIG. 6, if the soot filter is ready for regeneration, thenthe method advances to 100, where process steps 86 through 94 of method76 (described above, illustrated in FIG. 5) are enacted. However, if itis determined that the soot filter is not ready for regeneration, thenthe method advances to 102, where an alternative method for deliveringfresh air to the intake manifold during closed-throttle conditions isenacted. In one non-limiting embodiment, the alternative method maycomprise delivering fresh air to the intake manifold via a secondthrottle valve, as described below.

FIG. 7 illustrates a third example method 104 for providing intake airto an engine in a vehicle. The method may be enacted via an electroniccontrol system (e.g., electronic control system 54) coupled to one ormore sensors and electronically controlled valves, as described above.For example, method 104 may be enabled via the configuration shown inFIG. 3.

Method 104 begins at 78, where a mixture of fresh air and treatedexhaust is formed. The fresh air may be drawn from an air cleaner, whilethe treated exhaust may be drawn from an exhaust flow of the engine,downstream of an exhaust-aftertreatment catalyst and downstream of asoot filter. The method then advances to 106, where the mixture of freshair and treated exhaust is compressed. In one embodiment, the mixturemay be compressed via a turbocharger compressor. The method thenadvances to 108, where the MAP is sensed. The MAP may be sensed via anair-pressure sensor coupled to the intake manifold, for example. At 110,it is determined whether the MAP is greater than a lower threshold. Ifthe MAP is greater than the lower threshold, then the method advances to112, where the mixture is admitted to the intake manifold via the firstthrottle valve. Whether or not the MAP is greater than the lowerthreshold, the method advances to 114, where it is determined whetherthe MAP is less than an upper threshold. If the MAP is less than theupper threshold, then the method advances to 116, where fresh air isadmitted to the intake manifold via the second throttle valve. Method104 then returns to 78.

In the engine systems considered here, the MAP may be a surrogate orpredictor of engine load. More specifically, the MAP may increase asengine load increases, and decrease as engine load decreases.Accordingly, the upper and lower thresholds identified above may definethree engine-load conditions: a higher engine-load condition where themixture is admitted to the intake manifold via the first throttle valve,a lower engine-load condition where fresh air is admitted to the intakemanifold via the second throttle valve, and an intermediate engine-loadcondition where the mixture is admitted to the intake manifold via thefirst throttle valve and where fresh air is admitted to the intakemanifold via the second throttle valve. In this context, it will beunderstood that idle is a particular, limiting case of the lowerengine-load condition. During idle, substantially all of the intake airprovided to the engine may be drawn through the second throttle valve,i.e., the second throttle valve may function as an idle controller.

In other embodiments, the opening and/or closure of the second throttlevalve may be responsive to boost level. Further, the admission of freshair to the intake manifold may include adjusting the amount ofuncompressed fresh air admitted to the intake manifold via the secondthrottle valve based on the boost level provided by the intakecompressor. Such adjustment may, for example, include reducing anopening of the second throttle valve as the boost increases, andincreasing the opening of the second throttle valve as the boost leveldecreases. Likewise, the overall control method by include reducing anopening of the first throttle valve as the boost decreases, andincreasing the opening of the first throttle valve as the boost levelincreases. In one embodiment, adjusting the amount of uncompressed freshair may include increasing the opening of the second throttle valveduring TIP-out conditions of the engine. Further, the opening of thefirst throttle valve may be reduced on TIP-out.

In one embodiment, admitting the mixture to the intake manifold duringthe higher engine-load condition may comprise holding the secondthrottle valve closed. Conversely, admitting fresh air to the intakemanifold during the lower engine-load condition may comprise holding thefirst throttle valve closed. During intermediate engine-load conditions,the proportion of treated exhaust relative to fresh air supplied to theengine may be determined by the relative degree of opening of the firstand second throttle valves. Further, in one control embodiment, thecompressor may be provided a substantially equal proportion of treatedexhaust relative to fresh air during the higher, lower, and intermediateengine-load conditions.

FIG. 8 illustrates a fourth example method 118 for providing intake airto an engine in a vehicle. The method may be enacted via an electroniccontrol system (e.g., electronic control system 54) coupled to one ormore sensors and electronically controlled valves, as described above.For example, method 118 may be enabled via the configuration shown inFIG. 3.

Method 118 begins at 120, where the electronic control system senses anair-flow request of the engine system. In one embodiment, the air-flowrequest may issue from a pedal position sensor in the vehicle. Themethod then advances to 122, where it is determined if the air-flowrequest is less than a threshold. The threshold may correspond to aminimum amount of air flow where EGR can be tolerated withoutsacrificing combustion performance. If it is determined that theair-flow request is less than the threshold, then the method advances to124, where an EGR valve delivering EGR under current operatingconditions is closed. The method then advances to 126, where a firstthrottle valve (e.g., throttle valve 28 in FIG. 3) is closed. Under someoperating conditions, this action effectively traps a boosted air/EGRmixture upstream of the first throttle valve. The method then advancesto 128, where a compressor by-pass or compressed-air release valve inthe engine system is opened. At this point, the engine system isconfigured such that continued operation of the engine will pump downthe pressure in the intake manifold.

Accordingly, method 118 advances to 130, where the intake manifold airpressure is sensed. The intake manifold air pressure may be sensed via apressure sensor coupled to the intake manifold, or indirectly via a massair-flow sensor, or in any suitable manner. The method then advances to132, where it is determined whether the intake manifold air pressure isless than a threshold. If the intake manifold air pressure is not lessthan the threshold, then execution of the method resumes at 130.Otherwise, execution advances to 134, where the requested air flow ismaintained by modulating a second throttle valve in the engine system(e.g., throttle valve 60 in FIG. 3).

However, if at 122 it is determined that the air flow request equals orexceeds the indicated threshold, then at 136, the compressor by-pass orrelease valve is closed or maintained closed. At 138, the secondthrottle valve is closed or maintained closed, and at 140, the requestedair flow is maintained by modulating the first throttle valve.

It will be understood that no aspect of method 118 is intended to belimiting, as numerous variants of the method are contemplated. Forinstance, while the illustrated method shows, at 122, a determinationbased on the desired air-flow request which results in certain actsbeing taken, such a determination can be made instead based on arequested boost level or other operational parameter of the enginesystem. Further, in some embodiments where a check valve (e.g., checkvalve 62 in FIG. 3) is coupled in series with the second throttle valve,closure of the second throttle valve at 138 may be unnecessary.

FIG. 9 illustrates a fifth example method 142 for providing intake airto an engine in a vehicle. The method may be enacted via an electroniccontrol system (e.g., electronic control system 54) coupled to one ormore sensors and electronically controlled valves, as described above.For example, method 142 may be enabled via the configuration shown inFIG. 4.

Method 142 begins at 144, where a first fresh air flow is compressed anddelivered to a first throttle valve coupled to an intake manifold of theengine. The method then advances to 108, where the MAP is sensed. Themethod then advances to 110, where it is determined whether the MAP isgreater than a threshold. If the MAP is greater than a threshold, thenthe method advances to 146, where the first fresh air flow is admittedto the intake manifold via the first throttle valve, to 148, where anEGR flow is cooled in a heat exchanger, and to 150, where the cooled EGRflow is admitted to the intake manifold via the second throttle valve.Following 150, execution of the method resumes at 144.

Continuing in FIG. 9, if it is determined at 110 that the MAP is notgreater than the threshold, then the method advances to 152, where asecond fresh air flow is warmed in the heat exchanger, and to 154, wherethe second fresh air flow is admitted to the intake manifold via thesecond throttle valve. Following 154, execution of the method resumes at144.

As indicated above, the MAP may increase as engine load increases, anddecrease as engine load decreases. Accordingly, the threshold identifiedabove may define a higher engine-load condition and a lower engine-loadcondition. During the higher engine-load condition, compressed fresh airis delivered to the intake manifold via the first throttle valve whilecooled, EGR is delivered to the intake manifold via the second throttlevalve. During the lower engine-load condition, warmed fresh air isdelivered to the intake manifold via the second throttle valve.

Further, in one embodiment, the second fresh air flow may be switchablyadmitted to the heat exchanger via a control valve; the control valvemay be closed during the higher engine-load condition and opened duringthe lower engine-load condition. Accordingly, abrupt transitioning fromthe higher engine-load condition to the lower engine-load condition maycomprise releasing compressed air stored upstream of the first throttlevalve through a check valve. In this manner, the release of the storedcompressed air is responsive to an opening of the control valve.

In one embodiment, the first throttle valve may be held closed duringthe lower engine-load condition. In this manner, the second throttlevalve may be used to control intake air flow to the engine during thelower engine-load condition, and to control an EGR ratio for the engineduring the higher engine-load condition.

Various extensions of method 142 are contemplated as well. In oneembodiment, for example, based on the configuration shown in FIG. 4,opening first throttle valve 28, second throttle valve 60, and controlvalve 70 may be used to relieve excess boost pressure.

In another embodiment, a method for controlling an engine with EGRcomprises directing EGR from exhaust downstream of anexhaust-aftertreatment catalyst to mix with fresh air upstream of anintake compressor and upstream of a throttle valve, and in response toincreased throttling by the throttle valve, discharging the mixed EGRand fresh air from downstream of the intake compressor to the exhaustdownstream of the exhaust-aftertreatment catalyst.

It will be understood that the example control and estimation routinesdisclosed herein may be used with various system configurations. Theseroutines may represent one or more different processing strategies suchas event-driven, interrupt-driven, multi-tasking, multi-threading, andthe like. As such, the disclosed process steps (operations, functions,and/or acts) may represent code to be programmed into computer readablestorage medium in an electronic control system. It will be understoodthat some of the process steps described and/or illustrated herein mayin some embodiments be omitted without departing from the scope of thisdisclosure. Likewise, the indicated sequence of the process steps maynot always be required to achieve the intended results, but is providedfor ease of illustration and description. One or more of the illustratedactions, functions, or operations may be performed repeatedly, dependingon the particular strategy being used.

Finally, it will be understood that the articles, systems and methodsdescribed herein are exemplary in nature, and that these specificembodiments or examples are not to be considered in a limiting sense,because numerous variations are contemplated. Accordingly, the presentdisclosure includes all novel and non-obvious combinations andsub-combinations of the various systems and methods disclosed herein, aswell as any and all equivalents thereof.

1. A method for providing intake air via a throttle valve to a vehicle,comprising: forming a mixture of fresh air and treated exhaust, thetreated exhaust drawn from an exhaust flow of an engine downstream of anexhaust-aftertreatment catalyst; compressing the mixture upstream of thethrottle valve; and in a manner correlated to full or partial closure ofthe throttle valve, discharging the compressed mixture into the exhaustflow, downstream of the exhaust-aftertreatment catalyst.
 2. The methodof claim 1, wherein the compressed mixture is discharged into theexhaust flow upstream of a soot filter.
 3. The method of claim 1,wherein the compressed mixture is discharged into the exhaust flow inresponse to the full or partial closure of the throttle valve.
 4. Themethod of claim 1, further comprising restricting the forming of themixture in response to the full or partial closure of the throttlevalve.
 5. The method of claim 4, where restricting the forming of themixture comprises closing an EGR valve through which the treated exhaustflows en route to forming the mixture and where discharging the mixturecomprises opening a release valve variably coupling an upstream side ofthe throttle valve to a downstream side of the exhaust-aftertreatmentcatalyst.
 6. The method of claim 5, further comprising operating theengine with the release valve closed and the EGR valve closed.
 7. Themethod of claim 5, further comprising holding the release valve openuntil, and closing the release valve after, a pressure at the upstreamside of the throttle valve and a pressure at the downstream side of theexhaust-aftertreatment catalyst differ by less than a predeterminedamount.
 8. The method of claim 7, further comprising sensing thepressure at the upstream side of the throttle valve.
 9. A method forproviding intake air to an engine in a vehicle, the engine receiving theintake air via a throttle valve, the method comprising: forming amixture of fresh air and treated exhaust, the treated exhaust drawn froman exhaust flow of the engine downstream of an exhaust-aftertreatmentcatalyst; compressing the mixture upstream of the throttle valve via acompressor; closing the throttle valve in combination with opening arelease valve variably coupling an upstream side of the throttle valveand a downstream side of the compressor to a downstream side of theexhaust-aftertreatment catalyst; and closing an EGR valve through whichthe treated exhaust flows en route to forming the mixture.
 10. Themethod of claim 9, further comprising adjusting one or more of an extentof opening and a duration of opening of the release valve based on anoperating condition of the engine.
 11. The method of claim 10, whereinthe operating condition comprises an EGR ratio upstream of the throttlevalve.
 12. The method of claim 10, wherein the operating conditioncomprises a pressure at the upstream side of the throttle valve.
 13. Themethod of claim 9, further comprising closing the release valve when apressure at the upstream side of the throttle valve and a pressure atthe downstream side of the exhaust-aftertreatment catalyst differ byless than a predetermined amount.
 14. A system for providing intake airto an engine in a vehicle, the engine receiving the intake air via athrottle valve, the system comprising: a compressor configured tocompress a mixture of fresh air and treated exhaust and to deliver thecompressed mixture upstream of the throttle valve, the treated exhaustdrawn from an exhaust flow of the engine downstream of anexhaust-aftertreatment catalyst via an EGR conduit; an EGR valve coupledinto the EGR conduit, upstream of the compressor and downstream of theexhaust-aftertreatment catalyst, and configured to regulate how muchtreated exhaust is mixed into the fresh air; and a release valvevariably coupling an upstream side of the throttle valve to a downstreamside of the exhaust-aftertreatment catalyst.
 15. The system of claim 14,further comprising an electronic control system configured to open therelease valve in response to a closure of the throttle valve.
 16. Thesystem of claim 15, wherein the electronic control system is furtherconfigured to close the EGR valve in response to a closure of thethrottle valve.
 17. The system of claim 14, further comprising an EGRcooler configured to cool the treated exhaust flowing through the EGRconduit.
 18. The system of claim 14, where the exhaust-aftertreatmentcatalyst comprises a NOX-reduction catalyst.
 19. The system of claim 14further comprising a check valve coupled in series with the releasevalve and configured to prevent treated exhaust from flowingbidirectionally through the release valve.